1. Field of the Invention
The present invention relates in general to a parallel port and a method for controlling it, and more specifically, to a parallel port for connecting multiple devices and the method for controlling the same.
2. Description of the Related Art
As the glowing popularity of multimedia applications, scanners have been standard components of personal computer systems. At present, scanners are generally connected to a computer system through a print port, in order to avoid the inconvenience of having to plug in any SCSI card or any special interface card inside the computer and to simplify the installation so that the complicated tasks such as adjusting the I/O port, IRQ, and lack of expansion slot are no concern. It is very convenient to use the scanner by means of driver programs running in the computer system.
However, since the scanner is connected to a computer through a printer port, the printer can not be connected to the computer. In general, the voltages of the control signal on the control bus of the parallel port can be used for controlling the on-line and off-line states between the peripheral devices and the computer in order to use a single port to connect both printer and scanner to a computer simultaneously. For example, when the voltage level of the SLCT-IN signal line in the parallel port is low, the printer is connected and driven to operation, and when the voltage level of the SLCT-IN signal line in the parallel port is high, the scanner is connected and driven to operation. Although the above method can achieve the object of connecting both a printer and scanner to a computer simultaneously, the SLCT-IN control line is occupied, so no other peripheral device requiring control by all the four control signal lines can be connected.